This invention relates to a circuit board structure.
Many electronic instruments are composed of multiple circuit boards. Each circuit board comprises a substrate and various electronic components mounted on the substrate and interconnected by conductor runs that are incorporated in the substrate. Commonly, the circuit boards are arranged side-by-side in parallel relationship in a card cage, for example as shown in U.S. Pat. No. 5,030,108 (Babow et al). The circuit boards are inserted into the card cage through an opening at the front of the card cage, and are pushed towards the rear of this card cage. It is generally necessary that the circuit boards be interconnected with each other or connected to other equipment, and this may be accomplished by use of a backplane structure that extends across the rear of the card cage. Each circuit board includes at least one connector part at its rear edge and the backplane structure includes a complementary connector part that is engaged by the connector part of the circuit board when the circuit board is fully inserted in the card cage. A complex instrument might comprise several rows of circuit boards arranged one above the other. Circuit boards in a row at one level are connected to circuit boards at a different level through the backplane structure. This approach is subject to limitation in that the backplane structure must be able to accommodate planned expansion or else be replaced when expansion is necessary.
It is well known to construct a flexible electronic instrument having several different configurations by providing a mainframe unit that includes parts that are common to all configurations and installing plug-in modules in the mainframe unit. On installation in the mainframe unit, a plug-in module is connected to a backplane structure of the mainframe unit, and the backplane structure provides the necessary connections to the functional parts of the mainframe unit and to the other plug-in modules. Some of the modules might be functionally identical, while others might have different functions. This allows the capabilities of the instrument to be changed simply by addition of modules or replacing existing modules with different modules. However, in this type of instrument the number of plug-in modules that can be accommodated by the mainframe unit is limited.